Multiphase switching power supplies are used in many applications. For example, a multiphase buck converter may be used to generate a regulated output voltage (e.g., 1.8 V) from an input voltage (e.g., 3.3 V) having a magnitude that is greater than the magnitude of the output voltage.
An uncoupled-inductor (UI) power supply is a type of multiphase supply that typically has one filter inductor per phase, where the filter inductor of each phase is magnetically uncoupled from the filter inductors of the other phases.
For a specified output ripple voltage and transient response, a UI power supply has a relatively high efficiency, but also has a relatively large filter capacitance. The output ripple voltage is the voltage ripple that is superimposed on the regulated output voltage, and typically has a magnitude in the range of a few millivolts. The transient response is a measure of how fast the power supply stabilizes the regulated output voltage in response to a change in the load current. And the efficiency is a measure of the power consumed and dissipated as heat by the power supply itself; the higher the efficiency, the less power the supply consumes, and vice-versa. In a multiphase switching power supply, it is the power supply's switching circuitry that typically consumes most of the power consumed by the supply. Furthermore, the larger the filter capacitance, typically the larger and more expensive the power supply.
A coupled-inductor (CI) power supply is a type of multiphase supply that typically has one inductor per phase, where the inductor of one phase is magnetically coupled to the inductor(s) of at least one of the other phases.
Compared to a UI power supply for a specified given output ripple voltage and transient response, a CI power supply typically has a lower efficiency but a smaller filter capacitance.
Consequently, a designer may have no choice but to select a UI power supply for a system, such as a battery-powered system (e.g., a laptop computer), where, to extend the battery life and/or to minimize the system's heat generation, the efficiency of the supply is more important than the size and cost of the supply.
Conversely, a designer may have no choice but to select a CI power supply for a system, such as hand-held system (e.g., a cell phone or MP3 player), where, to fit the system within a relatively small housing and within a desired price range, the size and cost of the supply are more important than the efficiency of the supply.